The present invention relates to a process for producing carboxylic acid esters and to the catalysts suitable for catalyzing the esterification reaction. Acid-catalyzed esterifications and interesterifications are carried out as is known in the prior art, for example, with sulphuric acid or with hydrochloric acid as well as with soluble organic acids. Homogeneous acid catalysts are distinguished by particularly good activity. A disadvantage of the use of these prior methods and catalysts, however, resides in the poor separability of the desired product of esterification from the reaction product and, in particular, the need for an optionally distillative purification of the esterification product. This can cause undesirable discolorations of the product and/or product loss, particularly when higher-molecular reaction products are involved. It is also known to undertake ester formation in the presence of solid acid catalysts.
Such processes are described in EP-B-0192035 for cation exchange resins and in U.S. Pat. No. 5,502,240 for titanium containing zeolites as catalysts. According to this prior patent, phthalic esters are produced at temperatures of 210 to 230.degree. C.
It is therefore an object of the present invention to overcome disadvantages and drawbacks of prior known methods and to provide an improved process for producing carboxylic acid esters.
It is a further object of the invention to provide new catalysts which enable the catalytic reaction of carboxylic acids to form esters.